robin_astro

The region I have marked as the white rectangle. Based on your setup, it should neatly fit in your field of view with the zero order near the left edge

The series of absorption lines at the left end look like the Balmer series which suggests you are getting something at the blue end now but we really need the zero order in the same frame to calibrate it properly without guessing. Were you able to find the various spectra I talked about and chose the right one? This is what a wide field view (of Jupiter) through a grating looks like (From Christian Buil's page) http://www.astrosurf.com/aras/staranalyser/flat.jpg Notice how one of the spectra of Jupiter is much brighter than the others. this is the blazed first order and the one you want to get in the frame, together with the zero order Cheers Robin

The uploaded tiff image seems to be 1.5x larger than the camera sensor (4644x3120 compared with 3096x2080) has it been resampled somehow? Cheers Robin

Perhaps, but I dont think so. The Balmer lines and Telluric bands line up too well the original way round and the dispersion is about right for the second order (higher than calculated for the first order as expected.) The very deep band at ~7600A from O2 in the atmosphere is also good indicator and a common feature seen in all spectra taken from the ground. It could also explain the bias in the spectrum towards the IR (The blazed grating is optimised to preferentially select the wavelengths in the visible in the first order)

OK I think I know what has happened. It looks like you have captured the second order (the next spectrum out) This will be ~2x longer and much weaker than the first order, particularly in the blue. I think You will be surprised by the much shorter exposure you will need when you find the right spectrum ! Cheers Robin

OK it looks like you should just be able to fit the zero order and spectrum in the frame. Check the grating is rotated so the brighter blazed spectrum is to the right of the zero order (There is a mark on the Star Analyser filter cell to show approximately the correct orientation) and place the zero order near the left edge of the frame. To get you started, the blamer lines should then be roughly in the right place. For example H beta at 4861A should be ~4861/2.7 = 1800 pixels along from the zero order. It still does not explain the apparent low sensitivity in the blue (Do you have any other filters in the imaging train?) but we can worry about that once we have the full spectrum and zero order in the image Cheers Robin

Can you post a screen shot of the calculator with details of your current setup entered please Robin

OK I recommend rotating the grating so the spectrum is horizontal and moving the spectrum so the zero order (the star image) is visible as this is the 0 reference point we can use for the wavelength scale. You might need to reduce the distance of the grating to fit the spectrum and zero order in the frame. Use the RSpec calculator as your guide Cheers Robin

Also have a look at the tutorial videos on the RSpec website (It uses RSpec software but that was loosely based on Visuals spec and the steps are the same.) https://www.rspec-astro.com/more-videos/ there is a calculator there to help optimise your setup (based on my calculations) https://www.rspec-astro.com/calculator/ The slides from my BAA tutorial "Low Resolution Slitless Spectroscopy" might also be of use, downloadable from the bottom of this page https://www.britastro.org/downloads/15701 and Christian Buil's tips for using the Star Analyser http://www.astrosurf.com/aras/staranalyser/userguide.htm

Have a look at the image in the Star Analyser manual (I wrote it 😀) https://www.patonhawksley.com/resources Cheers Robin

This is more like what I would expect to see (in black) Are you using a mono or colour camera ?

Here's my stab at a wavelength calibration and line identification blue is your raw spectrum, red are the Hydrogen Balmer H alpha, H beta green are the telluric bands (O2 and H2O) The others are ripples in the camera response. If the calibration is correct, the lack of signal at the blue end is surprising. Normally H beta at 4863 A is near the peak of the curve. Is your spectrum correctly exposed with no saturated pixels in the spectrum? (Sirius is a very bright target and will need very short exposure.) Check also that you have to correct spectrum, The brighter one of the two nearest the zero order Sirius is also not an ideal target from the UK as it is low so the star image is likely to be large, reducing the sharpness of the spectrum and scintillation will distort the spectrum in short exposures. Cheers Robin

You have a mix of Hydrogen lines from the star, Telluric bands from the atmosphere and ripples from the spectral response from the camera but it is difficult to wavelength calibrate and identify them with any certainty without the zero order star as a reference point. (Is this outside the camera field?) Can you describe your setup (telescope, camera and the distance of the grating from the sensor) and also post an image of the raw spectrum please ? Thanks Robin

The 0.081 redshift puts the galaxy at about a billion light years away. As to what we might see, nobody really knows as we have not witnessed a supermassive black hole merger before. Cheers Robin

White Dwarfs sometimes also "eat" their planets. The elements they were made up of can be found in the spectrum of the star and detected using amateur equipment. https://britastro.org/observations/observation.php?id=20210831_232116_04a034fbfd0ae832 Cheers Robin

I got the idea to observe it after watching a video about this being a proposed target for JWST (link on my BAA page). The equipment I used is described on the BAA page. I just took a series of 1 minute exposures and measured the brightness in each one, relative to a non variable star in the same field (a standard technique for measuring variable stars) .The points in the graph are a 3 point moving average to smooth out the noise a bit. The transit time was from the NASA exoplanet archive website, also linked from the BAA page. This is very different from the usual exoplanet transits where the brightness just drops by a percent or two. Here it drops by half, but is it also much shorter compared with typical transits which can last for a couple of hours and a rather faint target (white dwarfs are not very luminous because they are so small) The diagram at the top of the graph shows the configuration inferred from the brightness drop but of course we cannot see that from here

Hi Mark, Most if not all galaxies have a supermassive black hole at their centre and if there is material nearby (dust, gas and even the odd star) it forms a disc and the material heats up as it spirals in producing emission at the Hydrogen alpha wavelength. (these galaxies are termed as having "Active Galactic Nuclei" Quasars and Seyfert Galaxies are examples of these. You can see this effect in this spectrum of M87, the black hole of which was famously imaged a couple of years back. https://britastro.org/observations/observation.php?id=20190411_213200_531d1ec6d134b3dc The width of the line (the doppler effect) is a measure of how fast the material near the black hole is orbiting as, if side on, we see the material both coming towards and away from us. (Jets can also be produced coming out from the poles which can have very high velocities) The orbital velocity can be used to estimate the mass of the black hole. The mass of the black hole is also closely tied to the total mass of the galaxy. In this case the two mass estimates do not agree. There is also some structure in the line ( a combination of different components moving at different velocities. You get a hint of this in my low resolution spectrum but the higher resolution spectra in the paper shows this in more detail) The authors of the paper interpret this as an indication that there are two black holes in close orbit round each other (There are other examples of this around so we know these exist) What is interesting in this case is the orbital period has been dropping rapidly (from a year to month) as energy is lost from the system as gravitational waves, suggesting an imminent merger. Note though this is hot off the press and not yet a peer reviewed paper. A merger has never been observed but if it does happen though, watch this space ! As the authors put it "Copious electromagnetic signals are expected, from radio to X-ray band, binary inspiral stage to post merger, and from locations such as black hole corona, (possible) jet, accretion disk, interstellar medium, etc. Neutrino production is also possibly detectable as a result of binary black hole coalescence. We would like to call the attention of the astronomical community to perform extensive multi-messenger, multi-band observation on this transient AGN source. Hopefully this campaign will be celebrated by many unprecedented discoveries in the years to come."

According to a paper published last week the 17th magnitude Seyfert Galaxy SDSSJ1430+2303/ (seen here in my spectrograph guider last night) contains a pair of supermassive black holes who's orbit is rapidly decaying and which are likely to merge in the next 3 years or possibly even sooner in just 100-300 days time. My spectrum (blue, overlaid on the latest spectrum in the paper in grey and corrected for the redshift) shows Hydrogen alpha emission at velocities up to +-12000km/s More on my BAA page here https://britastro.org/observations/observation.php?id=20220207_205606_9d5b2259183a3d41 Cheers Robin

The paper linked from that page has the dimensions for 611 Mhz and construction details (appendix 4) http://www.y1pwe.co.uk/RAProgs/MiniPulsarRx.pdf

The flat is there to deal with them but if you want to track them down you can work out which surface they are on from the size using eg a calculator like this https://astronomy.tools/calculators/dust_reflection_calculator Cheers Robin

The wavelength calibration looks about right but something has gone wrong with the response correction. I recorded a Uranus spectrum with the the ALPY 600 a couple of weeks back. It is in the BAA database. This is what the response corrected spectrum looked like https://britastro.org/specdb/data_graph.php?obs_id=11449 and this is what it looks like after division by the Pickles G2v spectrum, compared with the measurement from a professional paper

There are no Balmer lines in the reflectance spectrum (Uranus is not hot enough to produce these) There will be Balmer lines from the reflected sunlight but they are not obvious in G2v spectra at low resolution. If you don't know the dispersion of your setup (eg from past measurements of hot stars), you will have to guess the dispersion, either matching the features in the spectrum of 29Ari to the G0v template or you could use the Telluric bands in 29Ari (They are probably too mixed with the broad methane bands to be used in the Uranus spectrum) Cheers Robin

Nice Methane bands ! You can divide by a library G2v spectrum to produce the reflectance spectrum but would need to response correct the Uranus spectrum first. Cheers Robin

It culminates ~19:00UT at ~50 deg altitude from here in the north of England at the moment so should be a few degrees higher for you. https://airmass.org/chart/obsid:wright/date:2022-01-11/sso:p%3AUranus The problem could be the moon though at the moment which is very close tonight, only 4 deg away, moving away but getting fuller over the next few nights. Cheers Robin

WD 1856b is a Jupiter sized exoplanet in a close orbit around a much smaller white dwarf star, transiting every 1.4 days. (An interesting conundrum is how it managed to avoid being engulfed during the parent star's red giant phase). Actually, partially eclipses is perhaps a more apt description as it is a 56% deep grazing event and so is on the observing list for the JWST to measure the spectrum of the starlight passing through the planet's atmosphere. Although much deeper than typical exoplanet transits, measuring it did present some interesting different challenges due to its faintness (mag 17) and brevity (8 min). Here is an image of the star in question and my transit measurement. For anyone interested in following up the discovery of this unusual exoplanet and the planned JWST measurements. I have put some more information up on my BAA page https://britastro.org/observations/observation.php?id=20220106_172719_c34e10f42c4fc746 Cheers Robin